In modern medical facilities, radiology plays a crucial role in the diagnostic process. Because of this, high-quality medical imaging using display devices like liquid crystal display devices (LCD devices) is more important than ever before. Thereto, display devices are typically provided with a sensor and a controller device coupled thereto. One type of sensor is coupled to a backlight device, for instance comprising light emitting diodes (LEDs), of the LCD device. It aims at stabilizing the output of the backlight device, which inherently varies as a consequence of the use of LEDs therein.
WO2008/050262 discloses one example of such sensor for an LED-based backlight. The backlight device is herein provided with a transparent outcoupling plate overlying its surface from which light is emitted. Structures, such as prismatic grooves, are defined in the outcoupling plate, so as to guide light to a side face, where the sensor is located. Particularly, the outcoupling plate is designed so as to achieve light spreading in addition to the light guiding to a side face. This provides an improved uniformity of the light output of the backlight device. However, a stabilization of merely the backlight is insufficient for obtaining a high-quality display system, such can be for instance applied for medical imaging applications. Moreover, when considering such outcoupling plate in front of a display, light spreading is not desired.
EP1274066B1 discloses a display device wherein the sensing is applied in front of the display. Use is made herein of a light guide, f.i. a waveguide or fibre, to guide a portion of the light output to a sensor outside the viewing angle of the display. Light from a display area comprising a plurality of pixels is inserted into the light guide, for instance at one end of the fibre or into a continuous waveguide. Therewith, the area on the display blocked for light transmission is limited. Particularly, as disclosed in EP1274066, light rays traveling under a large angle to the axis of the light guide can be made to exit the structure, while ambient light cannot enter the light guide. By means of this small acceptance angle, it is avoided that ambient light enters the photodiode sensor without a need for shielding.
However, it is desired to further improve such a sensor system, i.e. sensor and light guide. One implementation shown in EP1274066 is that a end of a fibre is parallel to the output surface of the display and the fibre is bent. This is however not a most practical implementation.
Another such solution with a waveguide in front of a display is disclosed in WO2004/023443. The waveguide particularly includes a material of relatively higher refractive index surrounded by a material of relatively lower refractive index. A sensor is present at one edge of the waveguide. Alternatively, the waveguide may extend in four directions and the sensors may be present on four edges. This solution is intended (see example 3) for calibration measurements of an 10×10 passive matrix OLED display, wherein each pixel is turned on sequentially.
However, it is an object of the present invention to provide a sensor system that can be used for real-time measurements, e.g. while the display is in use. The solution of WO2004023443 seems not to be fit therefore. This solution is sensitive to receiving light from the ambient, such that the overall signal to noise ratio will be rather low.
It is therefore an object of the invention to provide a display device with a sensor suitable for real-time sensing (e.g. while the display is in use), with a high signal to noise ratio and without disturbance of an image emitted by the display.